The purpose of this proposal is to develop and define two assay systems for screening mutagenic or carcinogenic potential of environmental agents especially those that need to be metabolically activated. This first system is a host-mediated assay by culturing mammalian cells especially human cells in diffusion chambers (DC) and implanted into heterologous hosts. The induction of point mutagens, chromosome aberrations and sister chromatid exchanges of the target cells in DC after given the hosts with a compound under test will be used as indicators for assessing mutagenicity or carcinogenicity. The second system is a liver homogenate-mediated assay by incubating DC filled with the liver extract, cofactors and a compound under test with human cells in vitro. The same indicators will be used for measuring mutagenic or carcinogenic potential of a testing compound. Emphasis will be placed on standardization, definition, sensitivity and reproducibility of these assay systems. Known carcinogens, non-carcinogenic analogues and several unknown compounds will be tested by using these systems.